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The hacker responsible for a stunning attack on a Dutch company that issues security certificates for websites warned on Monday that he would "strike back again," after previously breaching another company earlier this year.

The hacker posted the warning on Pastebin under the handle "Comodohacker." The same account was used earlier this year to describe the attack on Comodo, which sells SSL (Secure Socket Layer) certificates, a crucial Internet security component used to secure encrypted communication between a computer and a website.

"Comodohacker," who has given press interviews, has described himself as a 21-year-old Iranian student, although that information is not confirmed. It is also suspected he could be Turkish, working alongside others.

Comodohacker said on Monday on Pastebin that he breached DigiNotar, an issuer of SSL certificates, in order to punish the Dutch government for the actions of its soldiers in Srebrenica, where 8,000 Muslims were killed by Serbian forces in 1995 during the Bosnian War.

More than 500 fraudulent SSL certificates were issued by DigiNotar after its systems were breached. A report released on Monday by DigiNotar's auditor, Fox-IT, found that more than 300,000 unique IP addresses may have accessed Google account information under the fraudulent certificate, potentially meaning the data exchanged with Google could have been intercepted.

Most of those IP addresses were located in Iran, which has raised questions about the connection between Comodohacker and perhaps the Iranian government, which closely monitors the Internet for anti-government dissent.

"That's the mystery" said Mikko Hypponen, chief research officer for the security vendor F-Secure. "How do we go from these rogue certificates to widescale interception of Iranian citizens?"

Hypponen said it is likely that the person claiming to be Comodohacker accomplished both the DigiNotar and Comodo hacks as claimed on Pastebin. The style of broken English is the same, and Comodohacker also apparently created certificates using Persian phrases he used during the Comodo hack, Hypponen said.

Comodohacker also wrote in his Pastebin note that he has gained access to four more "certificate authorities," which are entities or companies like DigiNotar and Comodo that issue SSL certificates. He claimed to have access to GlobalSign, a widely used certificate authority.

Steve Roylance, GlobalSign's business development director, said the company has started an investigation.

"There's no concrete evidence of anything that has happened so far," Roylance said. "We are taking this very seriously at the moment."

Comodohacker also wrote on Monday that he had in the past hacked StartCom, another certificate authority, but indicated that the attack didn't work.

StartCom's chief operating officer and CTO, Eddy Nigg, said on Tuesday that his company detected the attack in June but was able to block it before Comodohacker could issue any fraudulent certificates.